1. Field of the Invention
The present invention relates to a restart of an electronic apparatus upon recovery from a power failure.
2. Description of the Related Art
Conventionally, some of electronic apparatuses such as image forming apparatuses, which form an image on a recording material, and personal computers, incorporate a soft-switch power supply device therein. In such an electronic apparatus, when a user performs a power-off operation, control can be performed so that the power supply is stopped not immediately but after predetermined processing is performed, or remote control can be performed to turn on/off a main power supply of the electronic apparatus from a place away from the apparatus. Also, for a power supply switch for such an electronic apparatus, a rocker switch that maintains an on/off-state is not used, but an automatic-return momentary switch that comes into an on-state only during the switch being depressed, and returns to an off-state when the switch is released.
FIG. 9 is a block diagram illustrating a configuration of an image forming apparatus with a momentary switch employed therein, in which a conventional soft-switch power supply device is incorporated. An operation for starting an image forming apparatus when the power supply is turned on and an operation for shutting down the image forming apparatus when the power supply is turned off will be described with reference to FIG. 9.
Upon power being supplied to an image forming apparatus A from a commercial power supply B, an AC/DC converter 15 in a power supply device 10 is activated and generates a voltage source V1 (for example, +3.3 V). The voltage source V1 supplies power only to a switch SW1 in an operation part 13 and does not supply power to the other electrical components, and thus, only with the power supply from the voltage source V1, the image forming apparatus A remains in a nonoperating state.
Next, upon a user depressing the switch SW1 in the operation part 13 to make the image forming apparatus A operate, the voltage source V1 is applied to a capacitor C3 via a resistor R7, the capacitor C3 being charged with power.
Upon the capacitor C3 being charged with power, a base current flows in a transistor Tr3, turning the transistor Tr3 on. Upon the transistor Tr3 being turned on, a potential of a gate of the transistor Tr1 transitions to a ground level, making the transistor Tr1 enter an on-state. Upon the transistor Tr1 being turned on, a voltage source V2 is generated, power is supplied from the voltage source V2 to a CPU 14 in a controller 12 and a FAX unit 11.
The FAX unit 11 refers to a transmitter/receiver part that transmits/receives image data when the FAX unit 11 is connected to a telephone line. Also, the FAX unit 11 can be attached/detached to/from the image forming apparatus A, and FIG. 9 indicates a state in which the FAX unit 11 is attached to the image forming apparatus A.
Upon the CPU 14 being activated as a result of power being supplied from the voltage source V2 to the controller 12, the CPU 14 outputs a high level signal to a signal line S1, thereby making the transistor Tr2 enter an on-state. During the image forming apparatus A operating, the CPU 14 continues outputting the high level signal to the signal line S1. As a result, the transistor Tr1 is maintained in the on-state, thereby the operating state of the image forming apparatus A being maintained. With the circuit operation described above, upon a user depressing the switch SW1, power is supplied from the voltage source V2 to the image forming apparatus A and the FAX unit 11, thereby the image forming apparatus A staring operating.
Next, a circuit operation for shutting down the image forming apparatus A via a power-off operation will be described.
Upon a user depressing the switch SW1 to power off the image forming apparatus A and the FAX unit 11, the voltage source V1 is applied to the switch SW1, and also to the capacitor C3 via the resistor R7. As a result, a potential at a point a in FIG. 9 rises from a ground level to a potential of the voltage source V1, and this rising edge signal is input to the CPU 14 via a signal line S2. By means of the rising edge signal, the CPU 14 detects that the user depressed the switch SW1. Then, the CPU 14 starts a shutdown sequence for powering off the image forming apparatus A (for example, data storage, mechanical spacing operation, etc.).
Upon end of the shutdown sequence, the CPU 14 outputs a low level signal to the signal line S1, thereby turning the transistor Tr2 off. Upon the transistor Tr2 being turned off, the potential of the gate of the transistor Tr1 becomes the same as the potential of the voltage source V1, and thus, the transistor Tr1 is also turned off, thereby stopping the power supply to the controller 12 and the FAX unit 11, resulting in shutting down the image forming apparatus A.
For such soft-switch power supply control as described above, for example, Japanese Patent Application Laid-Open No. 2005-285041 proposes a power supply device configured so that on/off control of power supply is performed according to an external power supply control signal, the power supply device including a reset signal generation unit that reliably resets a microcomputer.
However, in the aforementioned soft-switch power supply device described in Japanese Patent Application Laid-Open No. 2005-285041, where power from a commercial power supply is shut down because of, e.g., a power failure, the electronic apparatus is shut down, too. Then, even when power is supplied again to the electronic apparatus from the commercial power supply after recovery from the power failure, the electronic apparatus remains in a nonoperating state unless the electronic apparatus receives an external signal to activate the power supply, and thus, the electronic apparatus cannot automatically transition to an operating state. Furthermore, where the electronic apparatus has a facsimile function, a problem arises in that the electronic apparatus is unable to receive fax after the power failure unless the electronic apparatus receives an external signal to activate the power supply or a user turns the power supply switch on again.